The present invention relates to a level shifter circuit and a display driver circuit which perform conversion into an output signal having a larger amplitude than an input signal.
In recent years, in a field of display devices, various methods of display devices have been developed, such as a liquid crystal display and a display using an organic EL element. Higher image quality and more gray-scale levels are required for these display devices, thus a voltage amplitude of a scanning signal and a gray-scale signal of the display device tends to increase. Therefore, a higher voltage is required for each output unit of a row driver (scanning driver) which drives scanning lines of the display panel, and a column driver (data drivers) which drives data lines of the display panel by the gray-scale signal.
On the other hand, high-speed transfer and low EMI (Electromagnetic Interference) or the like with a small number of lines is required for various control signals and video data signals which are supplied to the row driver and the column driver from the display controller. Thus, an amplitude of these signals tends to decrease. Also inside the row driver and the column driver, a miniaturizing process is adopted in order to suppress an increase in the area of a logic circuit which processes data that increases along with higher resolution and more gray-scale levels. Therefore, a power supply voltage of these logic circuits is in a trend to decrease.
Specifically for the low driver and the column driver, a lower voltage (for example, 1.5 to 2.0 V) is required for the input unit and a higher voltage (for example, 12 to 20 V) is required for the output unit. Especially the number of level shifter circuits for driving a high withstand voltage switch of a DA (Digital-to-Analog) converter increases according to the number of outputs and gray-scale levels of the display driver circuit. Thus a reduced area, lower power consumption, and a faster operation are required for the level shifter circuit.